‘Downton Abbey” has become a global cultural phenomenon, with its most recent (fourth) season averaging over 13 million viewers on PBS and winning fans in more than 200 countries.

But in the UK, the trials and tribulations of the Crawley family are regularly topped by another period drama — “Call the Midwife,” which has its third season premiere on PBS this Sunday at 8 p.m.

The 1950s-era series centers on Jenny Lee (Jessica Raine) and her fellow midwives Trixie (Helen George), Chummy (Miranda Hart) and Cynthia (Bryony Hannah) as they care for pregnant women and their babies in London’s impoverished East End.

And while it lacks the opulence of other traditional British costume dramas, creator Heidi Thomas credits its focus on small stories about rites of passage in human relationships — birth, loss and marriage — for its massive success in the UK (nearly 10 million viewers on average).

“These are all things that loom very large in individual lives but perhaps don’t have a spotlight shone on them in popular culture in the way that we do,” she tells The Post. “I think that is possibly the secret. It makes people feel as though their lives and their experiences are validated.”

“Call the Midwife” has enjoyed favorable critical reviews stateside and averaged 3 million viewers in its first season on PBS, growing slightly to 3.2 million viewers in Season 2. While that’s well above the PBS primetime average (2.3 million viewers), it’s far from matching its success in the UK — or that of “Downton’s” 13-million viewer average.

But Season 3 was the year that “Downton Abbey” emerged as a phenomenon, when ratings on PBS jumped 65 percent from the prior season — and the network is bullish that “Midwife” can see the same growth.

“I would love to see that happen with ‘Call the Midwife,’ ” says Beth Hoppe, chief programming executive and general manager of general audience programming at PBS. “It’s a different time period — gritty, inner-city London environment — but at the same time what I particularly like is the positivity, the optimism that you come away with.”

The drama’s historical roots — it’s based on the memoirs of Jennifer Worth — and theme of childbirth also make it a good fit for PBS’ older, female viewers, many of whom are sharing it with their daughters, Hoppe has found.

“You can always reach the largest audiences when you connect with them at an emotional level and I think ‘Call the Midwife’ does that in incredible ways,” she says.

The heartwarming stories continue in Season 3, which opens in 1959, with the midwives and nuns of Nonnatus House (a nursing convent) adjusting to their new home after being bombed out of their old space at the end of Season 2. New characters will be added, including Sister Winifred, a young nun from the country who has trouble adjusting to the midwifery life in London, and Patsy Mount, a secular midwife with a sad secret.

Fashion continues to play a role — while London is not yet feeling the effects of the Swinging Sixties, the costumes have been updated with shorter hemlines, slimmed down shift dresses, a pixie haircut for Trixie and even a female character in pants.

Whether American viewers come for the period clothes, the history lesson or the strong female characters, PBS is hoping there’s something for “Downton” fans to like in “Midwife,” which also strives for a lighter tone.

“This is a bit fresher, a bit lighter, possibly a bit more surprising and often very funny as well,” Thomas says. “In the middle of all the life and death and rites of passage, we do have a few laughs and I think that keeps people coming back for more.”